This invention relates to telephone systems in which shared analog signal facilities are interfaced to shared digital signal facilities.
U.S. Pat. No. 5,351,234, which has the same inventors as the present application, discloses a system in which video signals are distributed, and switched telephone service is provided, over a common broadband cable network. The disclosure of Pat. No. 5,351,234 is incorporated herein by reference.
FIG. 1 of this application presents a high level block diagram of the shared video and telephone cable system disclosed in the '234 patent. Reference numeral 10 generally refers to the video/telephone cable system. Major components of the system 10 include a cable transmission system 12, a transmultiplexer 14 and a digital 20 telephone switch 16.
Connections are provided between the cable transmission system 12 and n telephone subscriber locations. As indicated in the '234 patent, but not shown in FIG. 1, means are also provided to couple a plurality of video channel signals to the cable transmission system 12. The cable transmission system 12 carries n two-way analog telephone signal channels in a frequency division multiplexed (FDM) format within a frequency band assigned for telephone usage. The width of the frequency band containing the n channels is the same as the bandwidth provided for a video channel. The frequency band which carries the n FDM telephone channels in the cable system 12 is coupled via a modulator/demodulator (not shown) to an analog transmission facility 18 which interconnects the cable system 12 and the transmultiplexer 14.
The transmultiplexer 14 provides translation between the n two-way FDM channels carried on the analog transmission facility 18 and a like number of two-way digital telephone signal channels provided in a time division multiplexed (TDM) format in a digital transmission facility 20. The digital transmission facility 20 is connected between the transmultiplexer 14 and the digital switch 16. The digital switch 16 operates so that any one of the n telephone subscriber locations connected to the cable system 12 can be selectively connected for telephone communication with any other of the n subscriber locations. Also, the n subscriber locations can be connected through the digital switch 16 to subscriber locations maintained in an external telephone network.
The shared video/telephone cable system of the '234 patent provides for efficient use of the bandwidth allocated within the cable transmission system to telephone use. However, it would be desirable to reduce the cost of providing interfacing between the digital switch 16 and the two-way analog telephone channels provided to the subscriber locations.
It is therefore a primary object of the invention to provide an improvement in a system in which a broadband cable network is used to distribute telephone service to plural subscriber locations.
It is a further object of the invention to achieve a reduction in the hardware cost encountered in constructing a telephone system distributed over a broadband cable network.
It is yet another object to achieve concentration of telephone transmission facilities while having all switching and routing take place at a centralized location such as a telco central office.